diff --git a/lib/primitives/tx.js b/lib/primitives/tx.js
index 1a4832c1..4706525a 100644
--- a/lib/primitives/tx.js
+++ b/lib/primitives/tx.js
@@ -324,6 +324,20 @@ TX.prototype.getVirtualSize = function getVirtualSize() {
   return (this.getWeight() + scale - 1) / scale | 0;
 };
 
+/**
+ * Calculate the virtual size of the transaction
+ * (weighted against bytes per sigop cost).
+ * @param {Number} sigops - Sigops cost.
+ * @returns {Number} vsize
+ */
+
+TX.prototype.getSigopsSize = function getSigopsSize(sigops) {
+  var scale = constants.WITNESS_SCALE_FACTOR;
+  var bytes = constants.tx.BYTES_PER_SIGOP;
+  var weight = Math.max(this.getWeight(), sigops * bytes);
+  return (weight + scale - 1) / scale | 0;
+};
+
 /**
  * Calculate the weight of the transaction.
  * Note that this is cached.
diff --git a/lib/protocol/constants.js b/lib/protocol/constants.js
index 910a2afb..c066fbcd 100644
--- a/lib/protocol/constants.js
+++ b/lib/protocol/constants.js
@@ -422,6 +422,7 @@ exports.tx = {
   FREE_THRESHOLD: exports.COIN * 144 / 250,
   MAX_SIGOPS: exports.block.MAX_SIGOPS / 5,
   MAX_SIGOPS_WEIGHT: exports.block.MAX_SIGOPS_WEIGHT / 5,
+  BYTES_PER_SIGOP: 20,
   COINBASE_MATURITY: 100
 };